Household pets, such as cats or dogs, may be expected to live much or all of their lives indoors, in spite of their heritage as outdoor creatures. Pet owners often attempt to provide their pets with connections to the outside world by, for example, taking them outside on a walk or by giving them access to a window or door with a sight to the outdoors. For a cat, particularly, in an urban setting, access to a window may be its entire view of the outside world. Most pets, however, feel better when they can exercise not only their eyes, but also their acute senses of smell and hearing, as might be accomplished by access to a screened door or window. There are known enclosures which may be mounted in a window or door frame to allow the pet to be safely outside the building, where it can obtain a more complete outdoor experience, and some of these provide open screening. U.S. Pat. No. 4,445,459 to Julie, U.S. Pat. No. 4,989,546 to Cannaday, U.S. Pat. No. 5,148,767 to Torchio, and U.S. Pat. No. 5,167,202 to Bradford are exemplary. U.S. design Pat. D 549,401, issued to the present inventor and hereby incorporated in its entirety within this application, discloses a distinctly different construction from these, as does also design Pat. D 561,955 to Mc Donough. Each of these, however, suffers from a need for adjustable ventilation and other desirable improvements.